Remove redundant CHECK_CLOSED call

Author: tomasr8

Modules/_io/bufferedio.c

@@ -1383,8 +1383,6 @@ _io__Buffered_seek_impl(buffered *self, PyObject *targetobj, int whence)
         return NULL;
     }
 
-    CHECK_CLOSED(self, "seek of closed file")
-
     _PyIO_State *state = find_io_state_by_def(Py_TYPE(self));
     if (_PyIOBase_check_seekable(state, self->raw, Py_True) == NULL) {
         return NULL;